Certain fuels, such as diesel fuel, thicken in cold temperatures. Under certain conditions fuels may become so viscous that they cannot flow through the fuel lines or fuel filters. Such conditions pose problems for diesel powered trucks and other types of heavy equipment which must operate in cold weather.
Many prior art devices have been used for heating fuels. Some of these devices use hot engine coolant or engine exhaust as a heat source. The hot fluid is passed through a heat exchanger to heat the fuel. These devices have advantages over other types of heaters, such as electric heaters. This is because they use "waste heat" from the engine as the heat source and do not place any additional load on the electrical system of the vehicle.
A problem with prior art fuel heaters of the hot fluid type is that they do not provide for precise control of the fuel temperature. Some of these devices heat the fuel continuously regardless of whether heating is needed. If the fuel becomes too hot, loss of engine power will result. High fuel temperatures also adversely impact the operation of electronically controlled fuel injection systems. Such systems, which are common on many newer vehicles, require that the fuel be within a certain temperature range for efficient operation.
Other types of prior art fuel heaters, particularly those that use engine coolant as a heat source, are often connected in series with the cab heater of the vehicle. This approach further contributes to imprecision in the control of the fuel temperature because heating the fuel depends on the operator's use of the cab heater. The operator may not turn on the cab heater even though it is very cold. This may occur when the engine is allowed to idle for extended periods to avoid shutting it off. This is often done in very cold weather. If the fuel heater is inoperative the fuel may become too cold to flow and stall the engine. In warm weather the cab heater may be left on resulting in overheating of the fuel.
The installation of coolant heaters in series with the cab heater of the vehicle is also cumbersome. This is because the coolant hoses often have to be run long distances to the fuel heater. This also results in lower heating efficiency due to heat loss through the hoses.
A further disadvantage of fuel heaters that use exhaust or hot coolant as heat source, is that they are usually fully on or off. These devices do not allow for slight warming of the fuel. In addition, because the amount of heat required to affect a meaningful increase in the temperature of diesel fuel is relatively high, the heat exchangers tend to be large. This increases the weight of the device and often makes finding space to mount the unit a problem.
Thus, there exists a need for a diesel fuel heater that provides more precise and reliable control of fuel temperature and is more compact and light weight.